The invention relates generally to endoprostheses and, more specifically, to a sheath for protecting an intraluminal prosthesis and the patient when delivering and deploying the prosthesis to an area of a body lumen that has been weakened by damage or disease. The sheath of the present invention is also envisioned to be used with such prostheses as a graft for treating aneurysms of the abdominal aorta, or an intraluminal stent for repairing coronary arteries.
An abdominal aortic aneurysm (AAA) is an abnormal dilation of the arterial wall of the aorta in the region of the aorta that passes through the abdominal cavity. The condition most commonly results from atherosclerotic disease. Frequently, abdominal aortic aneurysms are dissecting aneurysms, that is aneurysms that are formed when there is a tear or fissure in the arterial lining or wall through which blood is forced and eventually clots, forming a thrombosis which swells and weakens the vessel. Abdominal aortic aneurysms do not cause pain, but are easily detected in a thorough physical examination. If the aneurysm is not detected and treated, it is likely to rupture and cause massive hemorrhaging fatal to the patient.
Treatment of AAAs comprises some form of arterial reconstructive surgery which commonly is referred to as a "triple-A" procedure. One such method is by-pass surgery, in which an incision is made into the abdominal cavity, the aorta is closed off above and below the site of the aneurysm, the aneurysm is resected, and a synthetic graft or tube sized to approximate the diameter of the normal aorta is sutured to the vessel to replace the aneurysm and to allow blood flow through the aorta to be reestablished. The graft commonly is fabricated of a biocompatible material that is compliant and thin-walled. Nylons and synthetic fibers have been found to be suitable for the construction of the graft. The mortality rate associated with this surgical procedure is favorable (less than 5%) when it is performed prior to rupture of an aneurysm. However, patients having an AAA typically are over 65 years of age, and often have other chronic illnesses which increase the risk of perioperative or post-operative complications. Those patients thus are not ideal candidates for this type of major surgery. Further, it has been pointed out that this procedure is not often successfully resorted to after an aneurysm has ruptured (the mortality rate increases to over 65%) because of the extensiveness of the surgery and the time required to prepare a patient for it.
Because of the aforementioned disadvantages to conventional surgical methods, another procedure was developed as an alternative to conventional, major surgery. This method also involves emplacement of a graft at the site of the aneurysm. The graft is deployed there by being routed through the vascular system carried by a catheter, wire or other device suitable for negotiating the vasculature. The graft and its deployment system often are introduced into the blood stream percutaneously with a femoral approach and the entire procedure can be performed using local rather than general anesthesia.
Once the graft has been positioned at the aneurysm, it is disengaged from the delivery system and can be affixed to the aortic wall both distally and proximally of the aneurysm. The graft is positioned in the vessel spanning the site of the aneurysm such that the walls of the graft are generally parallel to the walls of the affected area of the aorta. The aneurysm thus is excluded from the circulatory system by the graft rather than being resected altogether. If the aneurysm is a dissecting type and a thrombosis exists between the walls of the aorta, the now-excluded aneurysm may beneficially provide structural support for the graft.
Grafting systems often include an attachment system for deploying the graft. A tubular system, often referred to as a stent, may be fitted coaxially within the graft, and which can extend out of the graft at either or both the proximal and distal ends thereof. The attachment system often has a lattice or open weave structure, which can provide flexibility and promote rapid endothelial tissue growth through the structure once the graft has been deployed. The attachment system may include hook-like elements for penetrating the intimal walls to attach the graft to the aorta, or those hook-like elements may be provided on the graft itself.
The actual function of delivering the graft may be accomplished by inflating the balloon of a catheter by introducing pressurized fluid into a lumen of the catheter from a source external to the patient. Inflation of the balloon applies a force to the graft and any attachment system supplied therein which extends radially and presses the graft and attachment system into the vessel wall above and below the aneurysm. To avoid premature detachment of the graft and to prevent the attachment elements from damaging the vessels or halting the forward movement of the system while the graft is being routed to the treatment site, a protective capsule or sheath is often provided to protect and contain the graft until such time as deployment is desired.
The sheath helps hold the graft and stents onto the catheter and prevents direct contact of the elements of the combination with the walls of the vessel while the system is being advanced to the treatment site, thus protecting the vascular system of the patient from hazardous protrusions such as sharp edges on the stents. A rod or wire may be connected to the sheath and may extend proximally along the length of the catheter so that it can be manipulated by the physician exterior to the patient and retracted (proximally) at the time of deployment. Alternatively, the sheath can traverse the entire length of the catheter, and can be retracted (proximally) from outside the patient to expose the graft-and-stent combination. However, in either instance, the manipulative elements of the sheath may be relatively bulky and awkward to use, and may interfere with the precise placement of the graft and with the operation of the graft delivery system.
As used herein, reference to the "proximal" is toward the outside of the patient and away from the stent and graft while reference to the "distal" is toward the stent and graft on the balloon portion of the catheter. The proximal and distal references apply to directions in the vascular system such as the aorta.
It should be noted that sheaths are often used with other implantable devices, including intraluminal stents for delivery to the coronary artery. Percutaneous transluminal coronary angioplasty (PTCA) is a widely practiced procedure for treating coronary artery disease. In a typical PTCA procedure, a dilation catheter having an inflatable balloon is advanced through a patient's arterial system until the balloon crosses an atherosclerotic lesion. The balloon is inflated at a relatively high pressure so as to compress the atherosclerotic plaque of the lesion against the inside of the artery wall and dilate the artery. The balloon is then deflated to a small profile for removal from the patient's vasculature, and blood flow resumes through the dilated artery. To help prevent abrupt closure, dissection, or restenosis, a physician can implant an intravascular prosthesis or stent to maintain vascular patency inside the artery at the lesion. The stent may be delivered to the lesion site by a balloon catheter which then expands the stent to a larger diameter. The stent is left in the artery, either temporarily or permanently, at the side of the dilated lesion.
The stent may have protuberances on its outer surface facing the patient's lumen wall. Should such protuberances rub against the lumen wall during delivery of the stent, they may damage the lumen wall and cause the stent to be displaced from the catheter. The sheath holds the stent onto the catheter and prevents the stent from damaging the lumen walls while the stent is being delivered to the treatment site, thus protecting the vascular system of the patient from any sharp edges on the stents. However, as noted above, the manipulative elements of the sheath can be relatively bulky and awkward to use, and may interfere with the precise placement of the stent and with the operation of the catheter/stent delivery system.
In order for a stent to be used advantageously with the endoprosthesis systems described above for the treatment and repair of body lumen, an improved sheath is desirable for preventing the stent surface (possibly including hooks on the stent) from abrading the vessel wall. The improved sheath should keep the stent properly centered over the balloon catheter delivery system as the graft is deployed in the vessel. It would also be useful to remove the sheath from the graft without disturbing the precise placement of the stent over the balloon so that the graft may be properly implanted in the vessel. Although various sheaths have been proposed, none adequately provides all of these desirable features.
What is needed in the art of such implantable devices is a sheath which holds the stent tightly against a balloon delivery catheter, wherein the catheter can be removed without disturbing the precise placement of the stent over the balloon. The sheath should also be capable of being used with a variety of implantable devices, including various catheter/stent/graft combinations, for delivery anywhere in the body. The present invention satisfies this need.